Sung-Hyuck Kim

Acid Diffusion Length Corresponding to Post Exposure Bake Time and Temperature

The post exposure bake (PEB) step in lithography is important for fabricating good patterns when a chemically amplified resist is used. Hydrogen ions or acid is generated by a photoacid generator through light exposure. The generated acid diffuses and acts as a catalyst for chemical amplification during the PEB step. Acid diffusion length (ADL) affects the deprotection of a resist polymer, such that linewidth is affected by ADL. The common parameter that determines ADL is the acid diffusion coefficient D; thus, we must determine D accurately in order to obtain the actual linewidth. However, D cannot be unambiguously determined for the actual PEB temperature and time. ADL has become a critical factor for 100 nm patterns and below. Thus, the accurate ADL determination becomes an important issue for better linewidth prediction by simulation. To match ADL and PEB time and temperature, we attempted to determine the relationship between the PEB parameters and ADL. As a result, we obtained a reasonable ADL.

Efficacy and Safety of Dabigatran Versus Warfarin in Patients with Atrial Fibrillation : Analysis in Asian Population in RE-LY Trial

Efficacy and Safety of Dabigatran Versus Warfarin in Patients with Atrial Fibrillation : Analysis in Asian Population in RE-LY Trial

Mask Haze Measurement by Spectroscopic Ellipsometry

Haze formation on a reticle continues to be a major problem for the semiconductor industry. Haze can be formed on the outside pellicle and on the quartz backside of the reticle. The major component of haze is known to be ammonium sulfate that comes from the reticle cleaning process. Reticle materials, exposure wavelength, the roughness of a photomask and haze affect resolution and process latitude. Thus, haze on a mask surface needs to be studied. We need to know the usable lifetime of the reticle in terms of haze formation and how to prolong reticle lifetime by removing haze, if possible. In this paper, we introduce the haze measurement method by spectroscopic ellipsometry. The quantity of haze including the roughness of the reticle can be accurately measured by spectroscopic ellipsometry. Spectroscopic data shows an increase in the measured ellipsometry value with energy dose given to the reticle. We confirm that this signal increase is a direct result of the increase in haze quantity with exposed dose.

Fast topography simulation using differential method

The finite-difference time-domain (FDTD) is a standard method for simulating mask topography effects. Its algorithm is simple, robust, and easy to implement. However, the FDTD algorithm consumes a lot of computer memory and time. For full three-dimensional simulation of a small contact pattern, it takes several hours on a personal computer. To reduce computing time, we adopted the differential method (DM) which solves the Maxwell equations in spatial frequency domain. Speed is the main advantage of DM over FDTD. To verify the numerical accuracy of DM, we compared the aerial images of several line/space patterns whose topography effects are predicted by DM and FDTD. For the calculation of the aerial images, we used a vector model. For unpolarized light, the maximum intensities differ by about 7%. Having assessed the accuracy of DM, we now describe the simulation result of a two-dimensional pattern. The pattern mainly contains densely packed rectangles. The size of the simulation domain was taken to be 1.972 μm × 4.368 μm × 0.350μm on the mask scale where the first two numbers represent the size of the unit cell of the pattern. Illumination condition is KrF source, annular aperture of 0.85/0.55, and NA of 0.7. Estimated running time of FDTD for topography simulation was 180 days. However, DM took about 280 minutes. The resulting aerial image agreed within about 8% with an experimental image directly measured by an AIMS-FAB.

Reticle haze measurement by spectroscopic ellipsometry

This paper introduces the haze measurement method by using the spectroscopic ellipsometry. The quantity of the haze including the roughness of the reticle can be accurately measured by the spectroscopic ellipsometry. The haze inspecting method by this ellipsometric measurement does not give any damage to the sample, and it is not necessary to cover conductive material unlike to SEM, and it can get very small haze thickness difference by 0.2 /spl sim/ 0.3 nm. One of the other merits of HIME is that the actual inspection time is only a few second. We can also obtain the mask roughness map as a function of dose. More details and applications of haze measuring process are presented and discussed.

Reticle haze measurement by spectroscopic elipsometry

This paper introduces the haze measurement method by using the spectroscopic ellipsometry. The quantity of the haze including the roughness of the reticle can be accurately measured by the spectroscopic ellipsometry. The haze inspecting method by this ellipsometric measurement does not give any damage to the sample, and it is not necessary to cover conductive material unlike to SEM, and it can get very small haze thickness difference by 0.2 /spl sim/ 0.3 nm. One of the other merits of HIME is that the actual inspection time is only a few second. We can also obtain the mask roughness map as a function of dose. More details and applications of haze measuring process are presented and discussed.

Mask error enhancement factor variation with pattern density

The mask error enhancement factor (MEEF) minimization is much emphasized due to the reduction of the device technology node. The MEEF is defined as how mask critical dimension (CD) errors are translated into wafer CD errors. We found that the pattern density had influenced the MEEF and the MEEF changed with the pattern density variation. We also tried to obtain the 90 nm CD value with optimized diffusion length of the chemically amplified resist. It turned out that a very small diffusion length should be used to get the desired 90 nm line width with 193 nm. We used line and space (L/S) dense bars, 3 L/S bars only and isolated line pattern for the pattern density dependency and to obtain different MEEFs. In order to determine the MEEF by the various pattern densities, a commercial simulation tool, Solid-E, was used. We could obtain the minimum MEEF values for the different pattern densities by using this procedure.

Feasibility evaluations of alternating phase-shift mask for imaging sub-80nm feature with KrF

Alternating phase shift mask (AltPSM) is considered as one of the most promising technique in leading-edge lithography. Its optical performance can be verified by sub-100nm gate generation and guaranteed device properties, indicated as depth of focus (DOF) and on chip CD variation (OCV). Nevertheless, continuous gate reduction in logic device demands more high-qualified mask process and optimization of illumination to overcome resolution limit. As one of the solution, appropriate mask structure and OPC rule dependent on illumination condition are evaluated. Issues out of mask manufacturing and Cr-less PEPSM as substitution of PEPSM are also discussed. Besides, interrelation between issues of mask and optical characteristics are investigated and compared mutually. In the end of this paper, we propose the optimum mask type and opportune time for ArF lithography.

Application of Cr-less mask technology for sub-100nm gate with single exposure

Chrome Less phase lithography (CPL) may be the crucial technology to print 100nm node and below. CPL can apply to various design layers without causing phase conflicts, while phase edge phase shift mask (PEPSM) is beneficial for specific pattern configurations and pitches. Therefore, we tested the feasibility of CPL including phase grating and hybrid CPL. And we tested the two types of CPL such as mesa and trench structures to decide the proper shifter forming method. We evaluated pattern fidelity of CPL using simulation, aerial image measurement system (AIMS) and wafer printing. Finally, we will compare the optical performance between CPL and PEPSM for 100nm node SRAM gate.

Characteristics of the line width variation due to lens flare and its dependency on optical parameters

In this paper, we have investigated the line width variation depending on the amount of flare in DUV (248 nm) exposure tools and the optical parameters affecting line width variation due to flare. The field to be exposed was divided into two regions. One half has the open ratio of about 0% and the other about 100%. Since the open ratio means the ratio between the diffracted light by line and space patterns and the scattered light by flare, the change in open ratio corresponds to the change in the amount of flare. Also, since flare affects the line width variation to a limited range, we can decide the flare affected range (FAR) by measuring the line width from the boundary between 0 and 100% open ratio toward each direction.